This invention relates to a gas-filled switch which can accurately switch on and off a circuit of a distorted wave which includes higher harmonics.
In conventional gas-filled switches, an electromotive force which is generated by an arc current which flows in an arc-drive coil is utilized to rotate the arc so as to extinguish the arc during the rotation of the arc. In such operation, the drive force which rotates the arc is determined by the crest value of the arc current. This implies that the greater the arc current, the greater arc drive force is produced and the arc-extinguishing ability also becomes improved. The arc-extinguishing ability of the arc drive coil is usually designed in view of a case where the arc current is a sinosoidal wave. Therefore, in a circuit which has a thyrister rectifier in the load side by of the transformer, the arc current is small and the gradient of the sinosoidal curve from the zero level becomes sharp. Accordingly, the arc-extinguishing ability of the arc drive coil is small and the phase relationship between the arc current and the magnetic force becomes remote from the predetermined value so that the switching operation often becomes impossible.
Accordingly, it is an object of the present invention to provide a gas-filled switch which can overcome above-mentioned defects of conventional switches.
The present invention, in summary, discloses a gas-filled switch with an improved arc extinguishing characteristics. Such gas-filled switch comprises a gas-filled casing, a pair of electrodes disposed in the casing, a conductive retaining ring which encircles at least one of the electrodes, a permanent magnet of a cylindrical configuration mounted on the retaining ring, a conductive cylindrical body disposed in one end opening of the retaining ring, and an arc-drive coil encircling the cylindrical body and having one end connected to the conductive cylindrical body and other end connected to the electrode. Due to such construction, one root of an arc generated between electrodes is moved from one electrode to the cylindrical body so that the other root of the arc is subjected to the magnetic flux of the permanent magnet while the previous one root of the arc is subjected to the magnetic flux of the arc-drive coil, whereby the arc is effectively extinguished during the rotation thereof.